1. Field of the Invention
The present invention relates to a process for producing a resonant tag equipped with a resonant frequency circuit which resonates with a radio wave transmitted at a particular frequency from a detector.
2. Description of the Related Art
As is well known, resonant tag is a tag equipped with a resonant circuit which resonates with a radio wave transmitted at a particular frequency. Thus, when the resonant tag is brought into an area in which the radio wave of the particular frequency is transmitted, the resonant tag readily reacts to operate a buzzer or an alert lamp of a detector. Thus, to avoid shoplifting, the resonant tags are attached to goods and the like in department stores, discount stores, rental shops for video tapes, compact disk (CD) shops, etc.
Basically, a resonant tag is composed of a plastic film (as a dielectric), having a spiral (or a coil-shaped) circuit (hereinafter referred to as a “coil circuit”) on at least one face of the film, and a circuit for use as an electrode plate of a capacitor or another coil circuit which functions also as a capacitor on the other face of the film. If necessary, the resonant tag is laminated on a sheet of a base material such as a paper.
In addition to a resonant tag above, there is also proposed a resonant tag having no capacitor electrode section formed on the end portion of the coil circuit. In the proposed structure, coil circuits are formed on both faces of a plastic film in correspondence with each other to utilize the circuit itself as the capacitor electrode plate.
The following processes have been known as processes for producing a resonant tag and the like. In one process, the following steps are carried out. A metal foil such as an aluminum foil is laminated on a plastic film. A photosensitive resin is applied to a face of this metal foil. A negative film-having a predetermined circuit pattern is placed on the resin-coated face and is photosensitized. Non-photosensitive portion is developed and removed, and the exposed metal foil is then etched and removed, to form a circuit. In another process, the following steps are carried out. A metal foil is stamped out by a die stamp having a blade with a predetermined shape, to form a circuit, and the metal foil is thermally adhered to a base sheet (a sheet of abase material) at the same time when the stamping is conducted.
The present invention relates to an improvement of die stamping in the foregoing processes.
In the die stamping process, die must stamp out a metal foil that is formed into a roll while tine metal foil being rewound, and thermally adhere the metal foil to a base material, for the continuous working. Thus, the die stamping is applicable to laminate a metal foil with strength to some degree on a solid base material, whereas the die stamping is not so advantageous for other cases. Therefore, the die stamping is suitable for a printed circuit board using a relatively thick copper foil and including a phenol resin plate as a base material, etc.
A resonant tag is basically disposable and formed into a thin label, so that the resonant tag mainly adopts a reasonable thin aluminum foil as a metal foil, and a soft plastic film or paper as a base sheet. Thus, that aluminum foil may be broken or the base sheet may be also stamped out during stamping out or transferring the foil, so that the resonant tag using the die stamping has not been put into practical use in the current state.
In order to solve these problems, such a process is attempted that a metal foil is laminated on a carrier sheet which has thick thickness and a stamping die only stamps out the metal foil to transfer this metal foil onto a plastic film (as a dielectric) or a base sheet. However, this process has such problems as (1) the additional step of laminating the metal foil on the carrier sheet is required; (2) the metal foil and the carrier sheet must be separated with difficulty; (3) when the stamped-out shape is discontinuous such as round, the separation between the stamped-out portion and the non stamped-out portion is difficult; and the like.